1. Field of the Invention
This invention relates to bearings used in rotating cone rock bits.
More particularly, this invention relates to radially disposed thrust bearings used therein.
The rotating cone, which has rock-crushing teeth on the outer surface, is mounted on a short cantilevered journal shaft extending from a leg of the bit body. The end of the journal enters the base of the cone. Various designs of rock bits utilize one or more cones. Most generally, however, three cones are used. The rock bit is secured to the lower end of a drill pipe which is turned by a rotary table aboveground. As the bit turns, the teeth in the cones penetrate a rock formation. As the cones roll, a continuous repetition of teeth secured to the cone contact the rock formation to disintegrate the rock and bore a hole therein.
Very large downward forces are required to penetrate hard rock and, since the journal bearing shaft supporting the cone is of necessity angled downward, a considerable portion of the downward force is axial with respect to the journal bearing and must be borne or absorbed by a radially disposed thrust bearing positioned between the cone and the end of the supporting journal bearing.
A greater portion of the downward force is however radial with respect to the journal bearing and is carried by the journal shaft. A smaller radial spindle bearing shaft, concentric with and extending from the journal shaft, is positioned nearer the apex of the cone and also carries some of the radial load.
A grease seal, such as an O-ring, environmentally protects all the bearings.
Excessive wear or breakdown of the radially disposed thrust bearing will permit the cone to move axially toward the seal and toward a backface of the leg portion supporting the journal. If the seal becomes damaged or if the cone impinges the leg backface, then the useful life of the bit is abruptly curtailed.
2. Description of the Prior Art
Conventional practice provides a hard metal disc radially fixed within the cone, presenting a small round thrust face to the end of the spindle shaft. The end of the spindle is, of course, a matching thrust face. Because this bearing is essentially within the apex of the cutter cone, an increase in thrust bearing size requires a shortening of the length of the radial journal bearing to compensate for the large radially disposed thrust bearing.
A series of large ball thrust bearings, primarily used to retain the cones on the journals (located near the end of the main journal bearing), normally run unloaded, coming into bearing contact only in reverse thrust conditions to retain the cone axially on the spindle.
U.S. Pat. No. 3,549,214, held by the same assignee as the present invention, teaches an increase in thrust load capabilities by utilizing a radially disposed surface formed between the large journal bearing and the smaller spindle bearing extending therefrom. This annular, radially disposed surface is called a "snoochie" face by the assignee. By providing both an annular bearing between the "snoochie" face and the cone and a radially disposed disc at the end of the spindle bearing nearest the apex of the cone, an increased axial thrust load bearing capability is realized. Moreover, intermediate separate thrust elements used in both positions permit the wear to be distributed over twice the basic area of bearing, potentially extending bit life by postponing one failure mode. Several separate thrust elements are disclosed to be used between the cone and shaft at both thrust bearing locations.
U.S. Pat. No. 3,720,274 teaches the use of one or more separate thrust elements only at the "snoochie" face formed between the radial journal and spindle bearing.
Both of the foregoing patents avoid closely housing the separate thrust elements radially. U.S. Pat. No. 3,720,274 allows particularly large eccentric dislocations of these thrust elements.
U.S. Pat. No. 4,293,167 discloses the use of a spindleless rotating cone rock bit. Each leg of the bit supports a journal with only one radial bearing and one thrust bearing. The U.S. Pat. No. 4,293,167 patent effectively eliminates dimensional tolerance control problems associated with concentric main and spindle bearings wherein complementary bearing surfaces formed within an associated cone must be closely matched. However, the patent is silent relative to the use of intermediate bearing elements and no special provisions are made to distribute lubricant across the large thrust area as is now taught in the instant invention.
An advantage of the present invention over the prior art is the apparatus to provide a thrust bearing for a rock cutter cone of increased load bearing capacity and extended life expectancy.
Yet another advantage of the present invention over the prior art is the method to provide a first choice of bearing material in run against the stationary spindle shaft and an independent second choice of bearing material to run against the material of the rotating cutter cone.
Still another advantage of the present invention over the prior art is to provide for enhanced lubrication of the thrust faces and to insure the freest independent rotation of the intermediate thrust element by bearing that element radially within the cone.